In an injection molding machine, a mold clamping unit and an injection unit are arranged facing each other on a base, and the injection unit is moved back and forth for nozzle touching and release therefrom, with respect to the mold clamping unit. For this purpose, the injection unit is placed on a unit carriage which can move back and forth on the base.
The unit carriage includes a front supporting portion and a rear supporting portion, which conventionally are formed integrally with each other or connected by means of a plurality of frame members. The junction between these portions is required to have a structure capable of withstanding a compressive force or tensile force to which it is subjected during nozzle touching operation of the injection unit. Since various devices and cables are arranged intensively in this region, the junction is required to be built as simple as possible. Since the various cables are connected to the injection unit so that they can move back and forth together with the injection unit, they must be arranged lest they will not interfere with one another or run against some other members.
The injection unit is moved in the longitudinal direction by means of a nozzle touching mechanism. Usually, the nozzle touching mechanism includes a screw and a ball bearing nut, which are arranged so that the injection unit can be moved back and forth by driving the screw which is screwed in the ball bearing nut fixed to the unit carriage of the injection unit. This screw-nut portion is adequately protected by a flexible cover or the like, so that such a cover must be removed at the time of inspection or replacement.
According to the conventional arrangement and construction of the unit carriage and the nozzle touching mechanism, however, when removing the screw of the nozzle touching mechanism, the injection unit and the unit carriage have to be removed from the base. Thus, removing the screw not only requires the removal of other parts but also requires time-consuming centering and adjustment after remounting.
Furthermore, in the conventional injection unit, there is provided no means for supporting the portion of the screw which projects backward from the ball bearing nut. Thus, when the injection unit is in an advanced position where the projecting rear end portion of the screw is long, the screw tends to whirl, so that the screw and ball bearing nut may possibly suffer uneven wear.
Moreover, in the stage of adjusting of the injection molding machine, nozzle touching of the injection unit is sometimes made manually. In this case, the operator is always required to know the position of the injection unit so that he will be able to know the level of the touching pressure at least roughly even after the touching. Since the nozzle touching operation of the injection unit is controlled in accordance with the position of a dog relative to a limit switch or proximity switch, it is difficult to display the position of the injection unit continuously on a display unit by using intuitive means such as graphic forms as the display-unit is under the control of NC device. Therefore, the position of the injection unit is indicated only numerically or only by notifying the arrival of the unit at a predetermined position. Thus, it is difficult to know the relative position of the injection unit, and so still there is room for improvement for the operating procedure of the conventional injection molding machine.